A test, a trial or an experiment is an activity used to determine whether one (or several) technical component(s) (a mechanical setup, hardware or software), which is (are), speaking in general terms, the test object, is (are) functional in the context of particular framework conditions, and/or whether particular characteristics are present. Accordingly, the test object is the technical system that must be tested. Said test object can be the overall system (for example, a vehicle) or a part of the overall system (for example, a combustion engine, a drive system, an exhaust gas system or an exhaust aftertreatment system of a motor vehicle).
Some tests are used to examine actual, often transient, processes to which the test piece is subjected. They are often conducted in reproduced environments, i.e., simulated environments. Dedicated test benches are often used for these activities, such as, for example, an engine test bench, a drivetrain test bench or a roller test bench. These test benches enable to systematically subject the test object to specified environmental conditions, which means the test object is tested under said environmental conditions, and the reproducibility of a test process is thereby enabled. But test benches are also used for other purposes, such as for validating new or unknown processes in environments that could not be reproduced in reality for the test object, or only by means of very time-consuming and expensive processes. As the test environment is always an incomplete representation of the actual environment, any results obtained from testing must always be analyzed under consideration of the quality of the test environment, i.e. of the test bench and the simulated environment.
For example, the stated object of a test bench is often simulating real or fictitious (i.e., virtual) test runs of motor vehicles. In the following, these runs will be referred to as virtual test runs. For example, a combustion engine on an engine test bench or a drivetrain on a drivetrain test bench is subject to interface variables that are variable over time via a suitable interface (interface between a test bench that is available in reality and the simulation) and that would be experienced by the test object as a component of the overall system vehicle/driver/environment during a real test drive, e.g. of a real vehicle driving on the Großglockner High Alpine Road. Similarly, it can be interesting to subject the test object on the test bench to interface variables that are variable over time and may occur in course of an arbitrary, also a fictitious and not necessarily representable in reality, route. Such virtual test runs can be generated by means of different processes. For example, they can be measured during real test runs, or they are in part predefined and/or standardized (for example, standardized consumption cycles). However, such runs can also be calculated with sufficiently good quality in real time or approximately in real time (i.e., online) by means of virtual environments (a so-called X-in-the-loop test run, wherein “X” denotes the test object, for example, a combustion engine, drivetrain, etc.). Different measurements can be taken at the test bench during the execution of the virtual test run. To this end, the test object that is to be examined (combustion engine, drivetrain, battery, vehicle, etc., or components thereof) is loaded at the interfaces usually by a load unit (actuator), such as, for example, a dynamometer (mechanical actuator) or a battery tester (electrical actuator), whereby the test object is subject to the mechanical or electrical load that results from the virtual test run. Such test runs on the test bench enable the execution, in particular, of development or testing work on the test object that is situated on the test bench without the requirement of having to set up the overall system (e.g., a physical complete vehicle) in which the test object is normally incorporated as a part of the overall system, and without the necessity of first having to complete the test that is to be performed by means of a real test run with the real vehicle. Such tests on the test bench, moreover, have the advantage of good reproducibility and thereby better comparability of the results.
However, due to system limitations, a test bench is not capable of reproducing the conditions of a real test run with absolute exactness, but only with some limitation. Still, it is not always desired, nor required that the test object be subjected in all cases to these exact conditions. In some cases, the test object may be merely subjected to conceived, hypothetical conditions. According to the prior art, for example, current work on test benches focuses substantially, for example, on a high level of consistency of the mechanical and electrical power flows between the virtual and real test runs. Despite good correspondence of the particular measured variables over time that are taken on the test bench, often there are considerable differences with regard to some other measured variables over time. For example, it was found that, despite the good quality regarding the consistency of the mechanical power flows (such as, for example, speed and torque) and despite the use of identical measuring techniques for taking emission measurements during the virtual test run on the drivetrain test bench and on the roller test bench, when comparing the results to the real test run with the physical vehicle, the emission measurements (CO, NOx, . . . ), particularly in the partial load range, do not yield the same results. The reason is often to be found in different thermal and thermodynamic conditions, i.e., in the different temperature and heat flux density fields on neuralgic vehicle components. Said differences are due, among other reasons, to the different media flows (for example, air, water, oil, etc.) the test object is subjected to.
A real vehicle contains components and/or structural parts that can be exposed to different thermal loads. A related example is the combustion engine with a turbocharger and an exhaust gas system.
Components, such as a catalytic converter or particle filter, can also be arranged in the exhaust gas system. A thermal energy flow over the surfaces of the mentioned components and part components occurs in both cases (real or virtual test run). The electrical energy storage of a hybrid vehicle is another example. This component also interacts thermally with its environment/surroundings and is itself impacted by influences from the environment/surroundings (“conditions”). Correspondingly, an engine block or an exhaust gas system of a vehicle will engage in thermal exchanges with its environment in different ways, depending on the conditions and/or surrounding conditions. As a result, there are, accordingly, different transient component-temperature fields and heat flux densities (thermal energy flows) inside the component and on the component's surface. For example, in winter-like environmental conditions, a combustion engine will radiate a greater quantity of heat (cold road conditions, cold ambient air) than in summer-like environmental conditions (hot road conditions, hot ambient air). The heat transfer (heat flux densities) between a test object and the environment occurs based on the physical mechanisms of heat conduction, heat flux (convection) and heat radiation.
During a real test run with a real vehicle along a real route, heat transfer processes are in effect on the surfaces of the test object and/or part of the test object. Varying environmental and/or surrounding conditions are in effect that are characterized, for example, by the air pressure, humidity or temperature, resulting in effects such as spray water on the test object, etc. However, different environmental conditions are in effect at the test bench, which is one reason why the results from a virtual test run on the test bench deviate from a real test run. The generation (simulation and/or emulation) of within given conditions arbitrary heat transfer processes at the test bench has been of little interest thus far and/or has raised insufficient attention to date.
The cooling-air blowers, for example, that are often used on the test bench for generating an air flow over the test object, as well as test bench conditioning (for example, temperature adjustments in the test bench space) are typically insufficient to precisely emulate the real environmental conditions on the test bench. Cooling-air blowers are mostly used for reproducing the effects of engine cooling relative to the headwind speed. This is why said cooling-air blowers are often inadequately dimensioned, and/or they do not provide the required degrees of freedom. For example, frequently, the speed of the cooling-air blower is only controlled as a function of the traveling speed. By providing air conditioning in the test bench space, it is possible to regulate the air temperature and humidity in the environment of the test bench.
Further known is the use of conditioning equipment for the media at the test bench, such as intake air, coolant, oil and charge air. Said equipment is used, for the most part, on component test benches (engine, drivetrain, battery test benches, etc.). By means of such equipment the respective temperatures of the media is influenced and/or controls. The conditioning equipment for the intake air can, furthermore, influence the humidity and pressure of air.
A cooling-air blower and testing room air conditioning, as well as media conditioning receive setpoint settings, such as, for example, for temperature, humidity and pressure, from the test bench automation system. The setpoint are set one in form of a respective variable over time (e.g., temperature) and there is no interaction (in the sense of an X-in-the-loop simulation) in form of a retroactive effect on a virtual environment of the test object, wherein this can also be an anticipated, future environment. Moreover, there is the problem of finding the setpoint, i.e., the problem of setting a setpoint that reflects the virtual environmental conditions of the test object in a way that is close to reality.
Also known in the art are test bench apparatuses that have test object parts (such as, for example, an engine on an engine test bench) thermally encapsulated in order to better be able to emulate the thermal conditions. An apparatus of this kind can be derived, for example, from Krämer S., et al., “Shift Roll Testing On The Engine Test Bench,” MTZ-Engine Magazine, 2015, 76 (3), pp. 36-41. The auto body is simulated therein on the engine test bench in that the engine is arranged inside an enclosed engine encapsulation and the exhaust gas system inside an enclosed underbody encapsulation in order to simulate the thermal conditions inside the engine compartment and/or the underbody. An enclosure is provided, respectively, in an isolated housing (engine encapsulation, underbody encapsulation) that are fitted with blowers. The temperature in the engine and the underbody encapsulations is controlled by the blower. Accordingly, the solution as introduced herein allows for comparisons of the results from the measurements of the emissions on the engine test bench and the results from the roller test bench. However, this is insufficient for a realistic reproduction of the environmental conditions, because, on the one hand, a global temperature is adjusted in the engine and the underbody encapsulations and, on the other hand, the problem concerning correct setpoint settings persists. Consequently, various components of the test object, such as, for example, the engine block, turbocharger, cooler, exhaust gas system, etc. and/or parts thereof, have temperature distributions on their surfaces that are not consistent with the real or desired temperature distributions. Still, the temperatures of these components have a determinative influence not only on the heat transfer processes in form of heat energy fluxes (“heat flows”), but they also influence, for example, the emission behavior of the engine (for example, NOx, CO, etc.), whereby the undesired discrepancies between real and virtual test runs result. This means that the described method does not solve the problem of reproducing and/or of anticipating the thermal behavior of the test object during a real test run.
Therefore, patent DE 10 2013 213 863 B3 already describes a cooling system for a component, such as a combustion engine, that enables adjusting the temperatures on the component in that the component is ventilated by a blower matrix that is made up of a plurality of individual blowers. The cooling system therein enables adjusting different temperature zones (temperature fields) on a component. A target temperature for individual points is preset as a setpoint value, which is known from the very outset (meaning as early as the beginning of the test run), in form of a time curve that is adjusted by a controller unit via the blower matrix to examine, for example, the thermal strength of the component or of parts thereof. In contrast to conventional test bench apparatuses, this is an improvement, particularly with regard to the thermal conditions for a test bench experiment, and which may often be sufficient. However, the component temperature as a target variable for controlling conditions on the test bench disregards thermal transfer processes in form of thermal energy fluxes of the real test object in the different test environments. Accordingly, effects such as convection, heat radiation, etc. that play an important role at the components of the test object (physical vehicle) are therefore omitted from consideration on the test bench. Providing the temperature field of the surface of the test object and/or of the test object per se, as described in DE 10 2013 213 863 B3, neglects the thermal transfer processes and is therefore often insufficient for realistic test bench experiments in form of virtual test runs on the test bench.
Correspondingly, patent DE 10 2013 213 863 B3 is based on the very limiting assumption that the target temperatures on the selected measurement points are known as a function over time (i.e., they can be preset in advance as command variables of the control). Said values must be defined in advance, wherein such arbitrary determinations, however, do not allow generation of realistic environmental conditions, or said values would have to be established in advance over the course of an expensive and complex real test run. The patent DE 10 2013 213 863 B3 does not address the problem concerning the determination of setpoints.